Plastic tube formed by spiral winding of hollow section

ABSTRACT

A spiral-wound tube formed of a hollow section 1 is provided wherein the hollow section is joined together by extruder welding or gluing. The hollow section is coextruded and comprises an outer layer (2) of pastic with a homogenous surface and good weldability. An intermediate layer 3 is provided of a modified polymer and an inner layer (4) is also provided. The interior space defined by the tubular layers (2, 3, 4) is preferably rectangular in cross-section.

FIELD OF THE INVENTION

The present invention concerns a spiral-wound tube made of a hollowsection joined together by extruder welding or gluing.

BACKGROUND OF THE INVENTION

In an attempt to manufacture tubes of maximum strength and permanence ofshape with a certain consumption of material, spiral-wound tubes made ofa hollow section have been achieved, said section being joined togetherpreferably by extruder welding, but possibly also by means of gluing.

SUMMARY AND OBJECTS OF THE INVENTION

The object of the present invention is to lower the cost of manufacturefurther as well as to provide spiral-wound tubes with particularproperties on the different faces of the tube.

This is achieved by means of a spiral-wound tube which is characterizedin that the hollow section is coextruded and comprises an outer layer ofa plastic with a homogeneous surface and with good weldability, as wellas at least one inner layer of modified polymer.

According to the invention, the tube which is to be spirally wound, isformed with a layered tubular structure having an outer tubular layer ofplastic with a homogenous surface and an inner tubular layer of plasticwith a homogenous surface and an intermediate layer, between the outerlayer and the inner layer wherein the intermediate layer is also tubularand is preferably formed of a modified polymer. The outer layerpreferably consists of a UV-stabilized polyethylene, polypropylene,polyvinylchloride, or polycarbonate. The tubular portions define ahollow interior section which is preferably substantially rectangular incross-section. The tubular outer layer has a sidewall which forms aninner face of the spiral-wound tube and preferably consists of a polymerresistant to chemicals. The modified polymer which forms theintermediate layer is preferably foamed. This modified polymer may alsobe formed as polymer filled with minerals.

In the following, the invention will be described in more detail withreference to the accompanying drawing, wherein

FIG. 1 is a partly sectional side view of an exemplifying embodiment ofa spiral-wound tube in accordance with the invention, and

FIG. 2 shows an enlarged detail of a weld joint in the tube shown inFIG. 1.

The spiral-wound tube in accordance with the invention comprises aspiral-wound hollow section 1, whose side walls in the adjoining layersin the spiral winding are joined together preferably by extruderwelding, but alternatively possibly by gluing. In view of minimizing thematerial cost while, at the same time, retaining or improving theproperties of the finished tube, according to the invention, acoextruded hollow section 1, is used, which comprises an outer layer 2of a plastic with a homogeneous surface and good weldability as well asat least one inner layer 3 of a modified polymer.

If the starting point is a hollow section 1 which, besides thehomogeneous outer layer 2, also comprises an intermediate layer 3 ofmodified polymer and an inner layer 4 of a plastic with a homogeneoussurface, a tube with very good properties is obtained.

When the modified polymer consists of a foamed polyethylene,polypropylene, or equivalent, a tube is obtained which has aconsiderably lower weight but substantially unchanged ring strength ascompared with a conventional spiral-wound tube of the same diameter andmaterial thickness.

On the contrary, if it is desirable to improve the ring strength of thetube remarkably, whereas the weight of the tube is of secondarysignificance, the modified polymer may appropriately consist of apolymer filled with minerals. In this way it is possible to improve themechanical properties of the spiral-wound tube considerably withoutincreased material cost.

As the outer layer, it is appropriately possible to use UV-stabilizedpolyethylene, polypropylene, polyvinylchloride, or polycarbonate.

The best result is obtained if the hollow section 1 has a substantiallyrectangular cross-section, whereby the extruder welding can be carriedout by means of two extruder nozzles, one at the outer mantle of thetube and one at its inner mantle. The preheating of the side faces ofthe hollow section that are to be welded together takes placeappropriately by means of, for example, an electrically heated heatingbody or by means of blowing of warm air. The hollow profile 1 isspiral-wound around a relatively short mandrel, whose movement ofrotation takes care of the forward feeding of the hollow section. Theshifting of the ready-welded tube in the axial direction is taken careof by rollers, which are freely rotatable around stationary shaftsdirected radially to the main axis of the mandrel. As a result of thefact that the tube reaches its full strength as soon as the weld joint 5has cooled, just a very short mandrel is required.

By arranging the extrusion of the hollow section 1 so that the outerlayer 2 at one side, i.e. the side that forms the inside face in thefinished spiral-wound tube, consists of a polymer resistant tochemicals, a spiral-wound tube of very high-class properties is obtainedat reasonable cost of manufacture.

The manufacture of the spiral-wound tube in accordance with theinvention can be arranged either so that the coextruded hollow section 1is passed from the extruder nozzle through a cooling zone directly intothe machine in which the spiral winding and the extruder welding takeplace, or the hollow section 1 is gathered in large rolls forintermediate storage before the hollow section 1 is fed into the linefor the manufacture of the spiral-wound tube.

I claim:
 1. Plastic tube formed by spiral winding of a coextruded hollowsection joined together by extruder welding or gluing, the hollowsection comprising a first hollow section outer layer of a plasticmaterial with a homogeneous surface and with good weldability, a secondhollow section intermediate layer of modified polymer material, saidintermediate layer being surrounded by and concentric with said outerlayer and a third hollow section inner layer of a plastic material withhomogenous surface, said inner layer being surrounded by and concentricwith said intermediate layer.
 2. Plastic tube as claimed in claim 1,wherein the outer layer consists of UV-stabilized polyethylene,polypropylene, polyvinylchloride, or polycarbonate.
 3. Plastic tube asclaimed in claim 2, wherein the coextruded hollow section has asubstantially rectangular cross-section.
 4. Plastic tube as claimed inclaim 3, wherein the outer layer at the side wall of the first hollowsection that forms the inner face in the spiral-wound tube consists of apolymer resistant to chemicals.
 5. Plastic tube as claimed in claim 1,wherein the modified polymer is foamed.
 6. Plastic tube as claimed inclaim 1, wherein the modified polymer consists of a polymer filled withminerals.
 7. A plastic tube formed by spiral winding of a coextrudedhollow tubular section joined together by extruder welding or gluing,the hollow tubular section comprising:an inner tubular layer having aninner face surrounding a hollow space, said inner layer being formed ofa plastic with a homogenous surface; an intermediate tubular layer ofmodified polymer, disposed around and concentric with said inner layer;and an outer tubular layer of plastic with a homogenous surface and withgood weldability, said outer layer being provided around and concentricwith said intermediate layer.